sizeExtend amp signExtend

Question

olonho · Answer

not sure if I understand what s your point here When casting 16 bit to 32 bit value for example there are diffrent ways of performing this operation for negative values i e 0xffff can produce either 0x0000ffff ==65535 if seen as Int or 0xfffffff 1 if seen as Int signExtend explicitly specifies that later behavior is taken

zubzub · Answer

but how do you know when to extend and when to shrink

olonho · Answer

it depends on the API you re trying to call look at generated bindings to see what type is in method signature

zubzub · Answer

the size of the type is runtime dependend so how do you know at compile time if you need to extend or shrink

zubzub · Answer

or am I missing something

olonho · Answer

Could you provide an example so that we have better context

zubzub · Answer

say on one architecture size t is 16 bit on another architecture it s 64 bit

zubzub · Answer

I have a 32 bit int that I need to convert to size it

zubzub · Answer

in one case I need to narrow it in another case I need to extend it

zubzub · Answer

how would I know which one to choose if the choice depends on the runtime

olonho · Answer

any really usable platform where this happens

zubzub · Answer

depends if you want to support something like arduino uno which is 16 bit

zubzub · Answer

the thing is that the current approach only really works if you intend to compile code for 2 different sized architectures eg 32 amp 64

zubzub · Answer

which is fine for me btw it was mostly an observation

zubzub · Answer

one more question

zubzub · Answer

does the extend or reduce call always reduce extend size to the target type or does it do it regardless of the target type s size

zubzub · Answer

narrow

zubzub · Answer

ie if I call extend on a 32bit int and my target size t is 32bit at runtime will it make it 64bit or keep it at 32bit

olonho · Answer

note that stubs are generated per target so `sizeof size t ` is known at compile time

svyatoslav.scherbina · Answer

gt ie if I call extend on a 32bit int and my target size t is 32bit at runtime will it make it 64bit or keep it at 32bit These functions extend or reduce the size exactly to the target type So if you call extend on a 32bit int and your target size t is 32bit then it will keep it at 32bit

svyatoslav.scherbina · Answer

gt say on one architecture size t is 16 bit on another architecture it s 64 bit gt I have a 32 bit int that I need to convert to size it In this case you can convert your 32 bit `Int` to `Short` and then sign extend it to `size t` It seems to be the most safe approach

zubzub · Answer

ok thanks that makes things clear